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Activation ProductsActivation products are the radioactive atoms formed by the absorption of neutrons in and around the reactor core. For example, some of the trace quantities of cobalt and zinc in the water passed through the core become 60Co and 65Zn.
ActivityAttribute of an amount of a radionuclide. Describes the rate at which decays occur in it. The unit becquerel, Bq corresponds to the decay of one radionuclide atom per second.
Alpha particleA particle consisting of 2 protons plus 2 neutrons which is effectively a helium nucleus. They are emitted generally by heavy radionuclides.
Annual limits of intake, ALIsThese values are calculated from the committed effective dose equivalent, CEDE. They represent activity data that are equivalent to the annual dose limit produced by a particular radioisotope. This is an ICRP concept.
AtomThe smallest portion of an element that can combine chemically with other atoms.
Atomic numberThe number of protons in the nucleus of an atom. Symbol Z.
AWEAtomic Weapons Establishments. In the SERMG area they are at Aldermaston and Burghfield.
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BecquerelUnit of amount of radioactivity, Bq (see activity). 1 nuclear disintegration per second.
Beta particleA particle, emitted by a radionuclide, with mass and charge equivalent in magnitude to an electron. The electric charge may be positive, in which case, the beta particle is called a positron.
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Canopy effectThe channelling of rainfall down a surface which can lead to greater deposition of contamination on the ground. Leaves on trees or sloping roofs can generate such an effect.
CEDECommitted effective dose equivalent. The dose equivalents which relate to a 50 year integration period.
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DecayThe spontaneous transformation of a radionuclide. The decrease in the activity of a radioactive substance.
Decay productA nuclide or radionuclide produced by decay. It may be formed directly from a radionuclide or as a result of a series of successive decays through several radionuclides.
Derived limitsSee Generalised Derived Limits.
DoseGeneral term for quantity of radiation. See absorbed dose, dose equivalent, effective dose equivalent, committed effective dose equivalent, genetically significant dose. Frequently used for effective dose equivalent.
Dose equivalentThe quantity obtained by multiplying the absorbed dose by a factor to allow for the different effectiveness of the various ionising radiations in causing harm to tissue. Unit Sievert, symbol Sv. The factor for gamma rays, X-rays and beta particles is 1, for neutrons 10, and for alpha particles 20.
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Effective dose equivalentThe quantity obtained by multiplying the dose equivalents to various tissues and organs by the risk weighting factor appropriate to each and summing the products. Expressed in sieverts, symbol Sv. Frequently abbreviated to dose.
ElementA substance with atoms all of the same atomic number.
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FalloutThe global deposition of very fine particulate material following testing of nuclear weapons in the atmosphere during the period 1952-1963.
Fission ProductsFission is the division of a nucleus (e.g. 235U) into two (usually unequal) radioactive parts. These nucleii are called fission products.
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Gamma rayA discrete quantity of electromagnetic radiation emitted during radioactive decay that originates from the nucleus.
Germanium gamma ray SpectrometerA semiconductor detector that is most often used to measure gamma emitters because it offers the best energy resolution of any device.
Generalised derived limitsThese are general secondary standards, derived from the primary dose limits, which are used as cautionary indicators for materials of environmental significance. They are quoted for specific radionuclides and are expressed in activity units per unit mass, unit volume or unit time. They express a value that will virtually guarantee compliance with legislation dose limits. Fractional GDLs are summed for different radioisotopes to give an assessment of the overall effective dose equivalent.
GrayA measure of absorbed dose being the amount of energy imparted to unit mass of matter such as tissue. Symbol Gy. 1Gy = 1 joule per kilogram.
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Half-lifeThe time taken for the activity of a radionuclide to lose half its value by decay. Symbol t?.
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ICRPInternational Commission on Radiological Protection.
IonElectrically charged atom or grouping of atoms.
IonisationThe process by which a neutral atom or molecule acquires electric charge. The production of ions.
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Mass numberThe number of protons plus neutrons in the nucleus of an atom. Symbol A.
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NeutronAn elementary particle with unit atomic mass and no electric charge.
NucleusThe core of an atom, occupying little of the volume, containing most of the mass, and bearing positive electric charge.
NuclideA species of atom characterised by the number of protons and neutrons and, in some cases, by the energy state of the nucleus.
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Order of magnitudeQuantity given to the nearest power of ten.
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RadiationThe process of emitting energy as waves or particles. The energy thus radiated. Frequently used for ionising radiation in the text.
RadioactivePossessing radioactivity.
RadioactivityThe property of radionuclides of spontaneously emitting ionising radiation normally associated with nuclear decay to another nuclide.
RadonAn unstable, chemically inert, heavy gas produced during the decay of natural uranium and thorium. Radon and its daughters accumulate in soil and may be drawn into dwellings through slight under-pressure. Radon activity generally represents the main contribution to the dose received by members of the public.
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Scintillation counterA device containing material that emits light flashes when exposed to ionising radiation. The flashes are converted to electric pulses and counted. The number of pulses is related to dose/activity
SievertSee effective dose equivalent. An S.I. unit of radiation dose.